One of the known processes for producing cast articles in the form of sheets, plates, lenses and the like, having poor thermoplastivity, is generally called "cast polymerization." This cast polymerization process comprises the steps of charging a monomer and/or prepolymer to be cast into a mold, polymerizing the monomer and/or prepolymer by a suitable polymerization means and releasing the resulting cast polymer article from the mold.
As material for the mold, glass combines convenience in use, economy and proper workability for the production of cast polymer articles in the form of a plate, a sheet, a lens and the like.
However, when used in a cast polymerization process a mold made of glass has various disadvantages. One that is when the cast article of synthetic resin strongly adheres to the glass, release of the cast article from the mold becomes difficult. It is important to be able to easily release the cast article from the mold, because, if mold release is difficult, it becomes a bar to the practical application of such process. That is, much time will be required for the removal of the cast product from the mold, thereby decreasing efficiency in production. And more, in releasing cast articles which adhere strongly to the mold, they are often damaged, especially on the surface. This is a fatal defect from a commercial viewpoint.
So-called "lubricants" or "release agents" are generally used to make it easier to release the cast articles from the surface of the mold-cavity. A large number of various types of silicone-series lubricants have been developed and used. One of the most popular lubricants is polysiloxane (or silicone oil). In the prior art processes, however, polysiloxane or silicone oil was simply coated on the surface of a mold-cavity, or alternatively, the coated polysiloxane was baked at a temperature as high as at least 350.degree.C to result in hardening. In case a synthetic resin material having strong adhesion to glass is used for cast polymerization, the mold on which polysiloxane or silicone oil is just coated without heating can be used only once. The reason is that when the mold is used in casting, the lubricant results in being removed from the mold surface.
Alternatively, when dimethyl polysiloxane is coated on the mold, followed by heating the coated mold at a temperature of 350.degree. C. or higher to harden the coating, the resulting polysiloxane film on the mold is damaged. As a result, when cast polymerization is carried out by using the mold having such polysiloxane film thereon, the cast polymer removed from the mold often has an unattractive surface, such as stripes, pock marks, uneveness, cloudiness and the like. Thus the above prior art processes are unsatisfactory in order to obtain a finished product having an optically smooth surface.
Another serious disadvantage of these prior art processes is that repeated use of the same mold is impossible.
Most synthetic resin materials adhere very strongly to glass, and there have been, up to now, no useful processes which can provide acceptable mold release properties. Namely, there have been, up to now, no practical processes for cast polymerization by which cast polymer articles which adhere strongly to glass can be produced efficiently, using a mold made of glass, at least for the mold-cavity.